Towards High Efficiency Engine –
THE Engine
Bengt Johansson
Div. of Combustion Engines
Director of KCFP,
Lund University,
Sweden
What is a high efficiency?
Any text book on ICE:
• Ideal cycle with heat addition at
constant volume:
• With a compression ratio, Rc, of 60:1
and γ=1.4 we get an efficiency of
80,6%
• Why then do engines of today have
an efficiency of 20-40%???2
Outline
• What is high efficiency?
• Combustion, thermodynamic, gas exchange
and mechanical efficiencies. All four must
be high.
• Combustion to enable high efficiency
• HCCI
• Partially Premixed Combustion
• Can we do something about engine
design?
• Conclusions
Energy flow in an IC engine
FuelMEP
QhrMEP
IMEPgross
lMEPnet
BMEP
QemisMEP
QlossMEP
QhtMEP
QexhMEP
PMEP
FMEP
Combustion efficiency
Thermodynamic efficiency
Gas exchange efficiency
Mechanical efficiency
Net Indicated efficiency
Brake efficiency
Gross Indicated efficiency
FuelMEP
QhrMEP
IMEPgross
lMEPnet
BMEP
QemisMEP
QlossMEP
QhtMEP
QexhMEP
PMEP
FMEP
Combustion efficiency
Thermodynamic efficiency
Gas exchange efficiency
Mechanical efficiency
Net Indicated efficiency
Brake efficiency
Gross Indicated efficiency
MechanicaleGasExchangmicThermodynaCombustionBrake
***
Outline
• What is high efficiency?
• Combustion, thermodynamic, gas exchange
and mechanical efficiencies. All four must
be high.
• Combustion to enable high efficiency
• HCCI
• Partially Premixed Combustion
• Can we do something about engine
design?
• Conclusions
6
HCCI -Thermodynamic efficiency
Saab SVC variable compression ratio, VCR, HCCI, Rc=10:1-30:1;
General Motors L850 “World engine”, HCCI, Rc=18:1, SI, Rc=18:1, SI, Rc=9.5:1
Scania D12 Heavy duty diesel engine, HCCI, Rc=18:1;
Fuel: US regular Gasoline
SAE2006-01-0205
All four efficiencies
7
SAE keynote Kyoto 2007
Net indicated efficiency= ηC ηT ηGE
SI std
SI high
HCCI
VCR
Scania
+100%
Brake efficiency
SI std
SI high
HCCI
VCR
Scania
Net indicated efficiency= ηC ηT ηGE
SI std
SI high
HCCI
VCR
Scania
47%
Outline
• What is high efficiency?
• Combustion, thermodynamic, gas exchange
and mechanical efficiencies. All four must
be high.
• Combustion to enable high efficiency
• HCCI
• Partially Premixed Combustion
• Can we do something about engine
design?
• Conclusions
PPC - Diesel engine running on gasoline
0 2 4 6 8 10 12 1420
25
30
35
40
45
50
55
60
Gross IMEP [bar]
Gro
ss In
dic
ate
d E
ffic
ien
cy [%
]
Group 3, 1300 [rpm]
FR47333CVX
FR47334CVX
FR47336CVX
HCCI: ηi=47% => PPC: η
i=57%
12
Partially Premixed Combustion, PPC
13
-180 -160 -140 -120 -100 -80 -60 -40 -20
1000
2000
3000
4000
5000
6000Spridare 8x0.12x90 & 8x0.12x150, Iso-oktan, CR-tryck 750 bar, Duration 0,6 ms = 3.6 CAD
HC
[ppm
]
SOI [ATDC]-180 -160 -140 -120 -100 -80 -60 -40 -20
200
400
600
800
1000
1200
NO
x [
ppm
]
Def: region between truly homogeneous combustion, HCCI,
and diffusion controlled combustion, diesel
HCCI
PPC
CI
SAE 2004-01-2990
14
Experimental setup, Scania D12
Bosch Common Rail
Prailmax 1600 [bar]
Orifices 8 [-]
Orifice Diameter 0.18 [mm]
Umbrella Angle 120 [deg]
Engine / Dyno Spec
BMEPmax 15 [bar]
Vd 1951 [cm3]
Swirl ratio 2.9 [-]
Fuel: Gasoline or Ethanol
SAE 2009-01-2668
15
Efficiencies 17.1:1
4 5 6 7 8 9 10 11 12 1350
55
60
65
70
75
80
85
90
95
100
Gross IMEP [bar]
[%] Combustion Efficiency
Thermal Efficiency
Gas Exchange Efficiency
Mechanical Efficiency
SAE 2009-01-2668
16
4 6 8 10 12 14 16 18
50
55
60
65
70
75
80
85
90
95
100
Gross IMEP [bar]
[%
] Combustion Efficiency
Thermal Efficiency
Gas Exchange Efficiency
Mechanical Efficiency
Efficiencies 14.3:1
SAE 2010-01-0871
1717
4 6 8 10 12 14 16 180
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Sm
oke
[F
SN
]
Gross IMEP [bar]
2 4 6 8 10 12 14 16 180
0.1
0.2
0.3
0.4
0.5
0.6
Gross IMEP [bar]
NO
x [g
/kW
h]
Gross
Net
Brake
EU VI
US 10
2 4 6 8 10 12 14 16 180
1
2
3
4
5
6
7
8
9
10
Gross IMEP [bar]
CO
[g
/kW
h]
Gross
Net
Brake
EU VI
US 10
2 4 6 8 10 12 14 16 180
0.3
0.6
0.9
1.2
1.5
Gross IMEP [bar]
HC
[g
/kW
h]
Gross
Net
Brake
EU VI
US 10
Emissions
18
Emissions – different fuels
2 4 6 8 10 12 14 16 18 200
0.5
1
1.5
2
2.5
Gross IMEP [bar]
So
ot [F
SN
]
Ethanol
FR47330CVX
FR47331CVX
FR47333CVX
FR47334CVX
FR47335CVX
FR47336CVX
FR47338CVX
2 4 6 8 10 12 14 16 18 200
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
Gross IMEP [bar]
NO
x [g
/kW
h]
Ethanol
FR47330CVX
FR47331CVX
FR47333CVX
FR47334CVX
FR47335CVX
FR47336CVX
FR47338CVX
2 4 6 8 10 12 14 16 18 200
2
4
6
8
10
12
Gross IMEP [bar]
CO
[g
/kW
h]
Ethanol
FR47330CVX
FR47331CVX
FR47333CVX
FR47334CVX
FR47335CVX
FR47336CVX
FR47338CVX
2 4 6 8 10 12 14 16 18 200
1
2
3
4
5
6
7
8
9
10
Gross IMEP [bar]
HC
[g
/kW
h]
Ethanol
FR47330CVX
FR47331CVX
FR47333CVX
FR47334CVX
FR47335CVX
FR47336CVX
FR47338CVX
SAE 2010-01-0871
19
Efficiency with Diesel or Gasoline
5 10 15 20 25 3034
36
38
40
42
44
46
48
50
52
Gross IMEP [bar]
Bra
ke
Effic
ien
cy [%
]D13 Gasoline
D13 Diesel
D13 Diesel was calibrated by Scania to meet EU V
legislation.
Average improvement of 16.6% points at high load by replacing
diesel fuel with gasoline!
1.5 2 2.5 3 3.544
46
48
50
52
54
56
58G
ross In
dic
ate
d E
ffic
ien
cy [%
]
Abs Inlet Pressure [bar]
FR47338CVX
FR47335CVX
FR47334CVX
High dilution is needed
for high indicated efficiency
SAE paper 2010-01-1471
10%!
21
idealturbinemechanicalturbinecompressoridealcompressor WW __
4 6 8 10 12 14 16 180
5
10
15
20
25
30
35
40
45
50
55
Min
imu
m T
urb
o G
lob
al E
ffic
ien
cy [%
]
Gross IMEP [bar]
global
Turbo System Efficiency Requirement
Outline
• What is high efficiency?
• Combustion, thermodynamic, gas exchange
and mechanical efficiencies. All four must
be high.
• Combustion to enable high efficiency
• HCCI
• Partially Premixed Combustion
• Can we do something about engine
design?
• Conclusions
ICE research in Lund vs. time
1990 1995 2000 2005 2010 2015
23
CCV=Cycle to
Cycle
Variations in
Spark Ignition
Engines
GDI= Gasoline
Direct
Injection
2-S= Two Stroke
engine
VVT=Variable
Valve Timing
HCCI=Homogeneo
us Charge
Compression
Ignition
SACI=Spark
Assisted
Compression
Ignition
PPC= Partially
Premixed
Combustion
High efficiency thermodynamics:
Simulation results from GT-power
• Indicated efficiency 65,2%
• Brake efficiency 60.5%
Is 65% possible?
Any text book on ICE:
• Ideal cycle with heat addition at constant
volume:
• With a compression ratio of 60:1 and γ=1.4 we
get an efficiency of 80,6%
25
0 10 20 30 40 50 60 700
100
200
300
400
500
600
700
800
900
1000Peak cylinder pressure as function of compression ratio
Peak c
ylin
der
pre
ssure
[bar]
Compression ratio
Lambda = 1.2
Lambda = 3.0
There are a few drawbacks…
– Engine structure must be very
robust (if at all possible)
– Very high friction and hence
lower mechanical efficiency
26
There are a few drawbacks…
270 10 20 30 40 50 60 70
20
30
40
50
60
70
80
90Thermodynamic efficiency as function of compression ratio
Compression ratio
Therm
odynam
ic e
ffic
iency [%
]
No heat transfer losses
With heat transfer losses (Woschni)
How then make 60:1 usable?
• Swedish proverb: ”Den late förtar sig
hellre än går två gånger”
• Which according to google translate
means: ”The lazy man rather breaks
his back than walk twice”
28
Take it in steps!
How about
𝟔𝟎 = 𝟕. 𝟕𝟓If we divide the compression in two equal
stages the total pressure (and temperature)
ratio will be the product of the two
7.75:1 x 7.75:1=60:1
With a peak pressure of 300 bar the
pressure expansion ratio is 300:1 and hence
300^(1/1.4)=58.8.1 in volume ratio
(gamma=1.25 during expansion gives 96:1)
29
Split cycles from the past
30
From history: Compound Engine
Divide the expansion in
three cylinders with
same force, F, on each
piston.
The smaller cylinder
has higher pressure but
also smaller area
F=p*A
31
32
Split cycles from the present
33
Three step compression in production
• To run a smaller engine at
higher load turbocharging is
used. The engine is using two or
three shafts of which only one
can generate power
• High BMEP (up to 30 bar) results
with two-stage turbo
• Peak pressure 200 bar
34F. Steinparzer, W. Stütz, H. Kratochwill, W. Mattes: „Der neue BMW-Sechzylinder-Dieselmotor mit Stufenaufladung“, MTZ, 5,2005
Design criteria of engines today
Non-turbo SI engines
Load range 0-12 bar BMEP
Peak pressure during the
cycle 65-70 bar
Friction FMEP 0.25-0.5 bar
Highly turbocharged engines
Load range 0-30 bar BMEP
Peak pressure during the cycle
180-230 bar
Friction FMEP 1.2-2 bar
35
Divide the process into two cylinders
Low pressure cycle
• Use large naturally
aspirated engine designed
for 30 bar peak pressure
– Load range 0-5 bar BMEP
– Peak pressure during the
cycle 30 bar
• Friction FMEP 0.05-0.1 bar
High pressure cycle
• Use small engine with 300
bar peak pressure feed by
the large engine
– Load range 35-80 bar BMEP
– Peak pressure during the
cycle 250-300 bar
• Friction FMEP 1.2-2.2 bar
36
Principle layout
2 stroke- 4 stroke- 2 stroke
37
Operating cycle 2+4+2 stroke
38
Inlet
Inlet
Inlet
Compression Expansion
Compression
Compression
Expansion
Expansion
Exhaust
Exhaust
Exhaust
TDC TDCTDC
TDC
TDC
TDC TDC
TDC
TDCTDC BDCBDC
BDC BDC
BDCBDC
BDCBDC
1
1
3
3
2
2
4
4
Inlet
Compression
Expansion
Exhaust
Pre
ssure
Combustion
Principle layout
4 stroke + 4 stroke
39
Operating cycle 4 + 4 stroke
40
Inlet
Inlet
Inlet
Inlet
Compression Expansion
Compression
Compression
Compression Expansion
Expansion
Expansion
Exhaust
Exhaust
Exhaust
Exhaust
TDC TDCTDC
TDC
TDC
TDC TDC
TDC
TDCTDC BDCBDC
BDC BDC
BDCBDC
BDCBDC
1
1
3
3
2
2
4
4
Pre
ssure
Combustion
DOUBLE COMPRESSION EXPANSION ENGINE CONCEPTS: A PATH TO HIGH
EFFICIENCY
Nhut Lam, Martin Tunér, Per Tunestål, Bengt
Johansson, Lund University
Arne Andersson, Staffan Lundgren, Volvo Group
SAE 2015-01-1260
Conceptual design 4-4
42
SAE 2015-01-1260
SAE 2015-01-1260
43
Simulation setup, DCEE concept
- 2 models
Unit DCEE λ=1.2 DCEE λ=3.0
Bore, HP cylinder mm 95
Stroke, HP cylinder mm 100
HP-cylinder displacement dm3 0.71
CR, HP cylinder - 11.5:1
Bore, LP cylinder mm 317 249
Stroke, LP cylinder mm 100
LP-cylinder displacement dm3 7.9 4.9
CR, LP cylinder - 100:1
EGR % 0
CAC temperature K 350No
intercooling
Simulation engine speed rpm 1900
High Pressure cylinder
44
SAE 2015-01-1260
Low Pressure cylinder
45
SAE 2015-01-1260
Combined
46
SAE 2015-01-1260
Heat Transfer
• To reduce heat transfer:
– Reduce heat transfer coeff., h
– Reduce surface area, A
– Reduce gas temperature
– Increase wall temperature
47
Wall surface area
48
0 1 2 3 4 5 6 7 8 90
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Cylinder volume [dm3]
Are
a [m
2]
Wall surface area as function of cylinder volume
DCEE, lambda 1.2
DCEE, lambda 3.0
CI, lambda 1.2
CI, lambda 3.0
SAE 2015-01-1260
Area/volume-ratio
49
0 1 2 3 4 5 6 7 8 90
200
400
600
800
1000
1200
Cylinder volume [dm3]
Are
a/V
olu
me [m
2/m
3]
Wall surface area per volume as function of cylinder volume
DCEE, lambda 1.2
DCEE, lambda 3.0
CI, lambda 1.2
CI, lambda 3.0
SAE 2015-01-1260
Heat transfer losses
50
SAE 2015-01-1260
51
Estimation of friction mean effective
pressure, FMEP
0 50 100 150 200 250 3000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8FMEP as function of PCP
FM
EP
[bar]
PCP [bar]Designed engine peak cylinder pressure
Naturally aspirated SI-engine @
2300 rpm
Traditional heavy duty
turbocharged CI engine
HP cylinder,
DCEE-concept
LP cylinder,
DCEE-concept
•Friction is assumed to scale with
Peak Cylinder Pressure, Pmax
•FMEP assumed to be 1.2 bar @200 bar Pmax
SAE 2015-01-1260
52
Mechanical losses
UnitDCEE,
λ=1.2
DCEE,
λ=3.0
Conventional,
λ=1.2
Conventional,
λ=3.0
Peak cylinder pressure
-LP cylinder bar 36 16
-HP cylinder bar 300
FMEP
-LP cylinder bar 0.21 0.09
-HP cylinder bar 1.8
Total FMEP bar 0.34 0.31 1.8
Net indicated work,
IMEPn
bar 8.8 4.3 12.9 6.3
Mechanical efficiency % 96.1 92.8 86.0 71.6
Resulting Efficiencies
53
SAE 2015-01-1260
Summary
• HCCI has shown high efficiency
– Up to 100% improvement in indicated efficiency vs. standard
SI combustion
– Modest combustion efficiency
– HCCI peaks at 47% indicated efficiency at around 6 bar
BMEP
• PPC has shown higher fuel efficiency
– Indicated efficiency of 57% at 8 bar IMEP
– Indicated efficiency of 55% from 5-18 bar IMEP
– With 70 RON fuel we can operate all the way from idle to 26
bar IMEP
• With an effective compression/expansion ratio
of 60:1 the split cycle concept shows 62%
indicated/ 56% brake efficiency potential
54
hT =1-1
Rc
g-1
High Efficiency Combustion
Engines – What is the limit?
“It all starts at 40 and ends at 60”(% engine efficiency that is, not life)
Prof. Bengt Johansson
Lund University
Thank you!
56
Towards High Efficiency Engine –
THE Engine
Bengt Johansson
Div. of Combustion Engines
Director of KCFP,
Lund University,
Sweden